This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have developed a technique dubbed Dose-Dependent Protein Oxidative Surface Mapping (DD-POSuM), wherein we oxidize a protein by continuous gamma radiolysis of water for different amounts of time under pseudo-first order reaction conditions. We then generate a series of single point kinetic approximations for the rate constants of oxidation for each oxidation target. Radiation dose-dependent changes in the rate constant of oxidation are indicative of oxidation-induced conformational changes, and allow us to examine these conformational changes with some structural resolution. Previous work using DD-POSuM has indicated that oxidation of Spo0F, a single domain response regulator involved in Stage 0 of the sporulation response pathway, undergoes a specific unfolding event upon oxidation;however, the apparent kinetics observed do not fit very well with the two-state model suggested by circular dichroism spectroscopy. We have some evidence that this conformational change is triggered by oxidation of Met81 to the sulfoxide. In order to test this hypothesis, we are utilizing chemical oxidation of methionine as well as site-directed mutagenesis.